Electric furnace regulator system



July 19, 1938. N R T EL 2,124,436

ELECTRIC FURNACE REGULATOR SYSTEM Filed Feb. 15, 1957 Irwverwtor: Numan R. Sba'nsel His Attorney.

Patented July 19, 1938 ELECTRIC FURNACE REGULATOR SYSTEM Numan R. Stansel, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application February 13', 1937, Serial No. 125,619

. Claims.

My invention relates to electric furnace regulator systems, more particularly to electric arc furnace regulator systems, and has for its object simple, reliable and low cost means for adjusting 5 the furnace electrode to maintain a predetermined furnace operating condition.

It is customary in control systems for are furnaces to use a separate direct current source of supply for the electrode adjusting motor, the elecl0 trodes themselves being ordinarily supplied from an alternating current circuit. As a result, in the'event of failure of the alternating current supply source, the direct current source is usually still available for actuation of the electrode. Furthermore, the regulating mechanism for controlling the electrode motor is ordinarily biased to a position to close the motor circuit for lowering operation. Consequently on failure of the alternating current supply source the regulator moves in accordance with its bias to a position to lower the electrode and the electrode motor is caused to operate whereby the electrode is lowered into the charge, which if molten, results in objectionable contamination with carbon and other impurities from the electrode. Sometimes an undervoltage device responsive to are voltage is provided for deenergizing the electrode motor so as to prevent this lowering of the electrode into the bath.

It is more particularly an object of my invention to provide regulating mechanism which is simple and reliable and which inherently prevents operation of the electrode motor upon failure of the alternating current supply source.

In carrying out my invention I provide a contact member for controlling the electrode motor, which contact member is actuated by the differential eifect of two operating coils, one of the coils being responsive to the voltage from the electrode to the bath and the other being connected across the alternating current supply source. The operation of the regulator is thus effected from the alternating current supply source.

Furthermore, I provide means for biasing the regulator to an intermediate neutral position so that in the event of failure of the alternating current supply source deenergization of the electrode motors is assured.

For a more complete understanding of my invention reference should be had to the accompanying drawing, the single figure of which shows in diagrammatic form an arc furnace regulator system embodying my invention.

Referring tothe drawing, I have shown my invention in one form as applied to an arc furnace l0 comprising a suitable crucible I for a metallic charge l2 and suitable carbonaceous electrodes |3, I4 and I5 extending into the crucible into arcing relation with the charge. While I have shown a three-phase furnace, it will be understood that my invention is applicable also to a single-phase furnace or a direct current furnace. The electrodes are each adjustable in a vertical direction to vary the length of the arc in any suitable manner. This adjusting means is shown diagrammatically for the electrode I5 only, but it will be understood that the other two electrodes are each equipped with the same or suitable regulating and electrode adjusting means. As shown, the electrode I5 is adjustable by a suitable direct currentreversible' electric motor I6 provided with a shunt field winding H which motor is connected to rotate a fixed gear wheel l8 having its bore threaded to receive a screw rod l9 attached to the electrode I5.

The armature of the electrode motor I6 is energized from a suitable direct current source of supply 20 through electromagnetic reversing switches 2| and 22 which are in turn controlled by the regulating mechanism 23. The electrodes of the furnace are electrically connected through a suitable transformer 24 to a three-phase source of supply 25.

The regulator 23 comprises a contact arm 26 pivoted at the point 26a and arranged to engage one or the other of two stationary contacts 21 and 28 to selectively energize the operating'coils 29 and 30 for the reverse switches 2| and 22' respectively. By means of two springs 3| and 32,

- shown as helical tension springs, or other suitable means, the contact arm 26 is biased to an intermediate neutral position, as shown in the drawing, in which neither of the contacts 21 and 2B is engaged. In this position of the regulator the coils 29 and 30 are deenergized and the reversing switches are in engagement with their lower contacts, as shown in the drawing, thereby closing a dynamic braking circuit for the armature of the electrode motor l6 through a resistor 33.

For actuation of the contact arm 26, an operating coil 34 is provided having a solenoid connected to one end of the contact arm. This coil is energized in response to the voltage drop from the electrode IE to the bath, or, in other words, in the arc furnace shown, to the voltage drop across the arc between the electrode and the bath. One terminal of the operating coil 34 is connected through a conductor 35 to the alternating supply conductor 36 leading to the electrode I 5 while the other terminal of the coil 30 is connected through an adjustable resistor 8? by means of the conductor 38 to the bath i2.

Acting in opposition to the coil 36 is a coil 33 which is connected through an adjustable gesistor it and a suitable voltage step-down. transformer Ail to one phase of the supply source 255. This phase is preferably the one, as shown, to

which the electrode 05 is connected. The coils 36 and 39, when energized, tend to lift their respective solenoids, which are shown connected to opposite ends of the contact member 25.

Another feature which I have disclosed is an anti-hunting or'damping means for the contact arm 26. This consists of two coils 42 and 43 positioned on opposite sides of an extension or portion 44 of the amt, this portion 44 being made of magnetic material and forming an armature for the two coils. The coils are electrically connected so as to be energized selectively by engagement of the contact arm with the stationary contacts 21 and 28 and when energized exert a force on the armature 44 in a direction to move the contact arm 26 back to the open circuit position shown in the drawing. Thus when the contact arm 26 engages the contact 28 the circuit is closed from the direct current supply source 20 through the conductor 45, contact arm,

conductor 46, the coil 43 and-conductor 41 to the supply source, whereby the coil 43 exerts a force to pull the contact arm away from the contact 28. In a similar manner, when the contact arm 26 engages the contact 2'! a circuit is closed for the coil 42 through the conductor ib, the contact arm, conductor 48, the coil 42 and conductor 41 back to the supply source 23. The action of the coils 42 and 43 results in deenergization of the electrode motor it slightly before the electrode has been adjusted the desired amount to allow for coasting of the motor in coming to rest and the further adjustment vof the electrode incidental thereto.

I In the operation of the device it will be assumed that the supply conductors 20 and 25 are connected through suitable switches, not shown, to their respective supply source and that the furnace is operating under the desired arc .voltage conditions, the charge I! being molten. The coils 3d and 39 then exactly counter-balance each other and the springs 3| and 32 hold the contact arm 26 in the position shown. It will be understood that the coils may be adjusted for a desired predetermined arc voltage condition by adjusting the resistors 31 and d0.

Assume now that the voltage across the are from electrode iii to the bath rises to a predetermined maximum value for some reason, for example, due to the slow burning by the arc of the lower end of the electrode whereby the length of the are slowly increases with resultant decrease in the currentin the electrode circuit and increase in the voltage across the arc. At this predetermined high voltage the coil 36 is energized sufiiciently to move the contact arm 26 upward against the force exerted by the coil 33 and also against the centering force applied by the springs 3i and 32.- Contact is thus made with the contact 28 whereby the coil 29 is energized and also the coil 83. The circuit for the coil 29 leads from the supply source 23 through conductor 45, contact arm 25, conductor 66, the coil 29 and conductor 63 back to the supply source 23.

The coil 23 moves the switch ii to its uppermost position whereby a circuit is closed for the greases electrode motor it which may be traced from the supply source 28 through conductor 50, the resistors 55 and 52, the switch M, the armature of the motor, switch 22 and conductor 53 back to the supply source. This causes the motor it to operate to lower the electrode i5 and in so doing the arc voltage is decreased. The adjustment is ordinarily performed very quickly and, as previously explained, the motor is stopped by the influence of the anti-hunting coil 63 to allow for the additional adjustment incidental to coasting of the motor.

In the event that the arc voltage becomes lower than a predetermined allowable minimum value, as might result for example by the addition of charge to the furnace whereby the arc is shortened and the voltage across it decreased, the force applied by the coil 34 is not great enough to counterbalance the coil 39 which thereupon moves the contact arm intoengagement with the contact 21 whereby a circuit is closed for the reversing switch coil 30. This closes a circuit for the motor l6 through the conductor 50, resistor 5|, switch 22, the armature of the motor, switch 2|, resistor 33 and conductor 53, whereby the motor is operated in the opposite direction to raise the electrode. This operation continues until the contact arm 26 is moved to the neutral position, as will be understood from the previous description of the lowering operation.

In each case, when the motor circuit is opened a dynamic braking'circuit is closed through the resistor 33, as shown in the drawing, whereby the motor i6 is brought quickly to rest.

The resistors 5| and 52 are provided for motor speed regulating purposes. It will be noted that both resistances are in circuit in series with each other and with the motor when the motor is operated to lower the electrode whereas the resistor 5! only is included in the motor circuit for raising operation. This provides greater torque for the raising operation whereby the adjustments are made with about the same speed in both cases.

In the event of failure of voltage of the alternating current supply source 25, it will be observed that both of the coils 3% and 39 are deenergized and consequently the contact arm 26 is held in the neutral position shown by the springs 3| and 32. If the failure of supply voltage occurs when the contact arm 26 is in engagement with the contact 21 or the contact 28 to effect a regulating operation, the contact arm is immediately pulled by the springs 3i and 32 to the neutral position, thus deenergizing the electrode motor. Therefore, operation of the electrode motor is eii'ectively prevented during the interval of alternating current supply source failure.

When the alternating voltage comes on again the two coils 3d and 39 are reenergized, the coil 39 as before, but the coil 36 with a higher voltage since no current is flowing. This voltage in fact is then the open circuit electrode voltage. Therefore, the coil 36 operates to cause lowering of the electrode l5 until it touches the charge,

When this occurs a very heavy current flows and the voltage from the electrode to the bath drops to a relatively low value. Thereupon the regulator is operated by the greater efiect of the coil 39 to reverse the electrode motor and raise the electrode until the desired arc voltage conditions are restored.

It should be observed that the furnace may be started by simply closing its supply circuit 2,124,488 through a suitable switch, not shown, whereupon the regulator operates to automatically lower the electrode into contact with the charge after which it is raised to establish the desired operating condition.

While the regulator is responsive directly to the arc voltage and operates to maintain the arc voltage at a desired value between predetermined minimum and maximum voltage limits, in so doing it maintains a predetermined constant current in the electrode circuit. This is because the current in the arc is proportional to the voltage across the arc, although inversely so.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric furnace regulator system comprising operating means i'or adjusting an electrode, control means for starting and stopping said operating means to adjust the electrode, said control means having an intermediate position in which said control means is inefl'ective to adjust the electrode, a pair of. opposed coils for operating said control means, connections for energizing one of said coils in response to an electrical condition of the electrode circuit, connections for energizing the other of said coils by the electrode supply source voltage whereby said control means is operated to effect adjustment 01' the electrode so as to maintain a predetermined relation between said electrical condition and the supply source voltage, and means responsive to failure of the electrode supply source for returning said control means to said intermediate position.

2. An 'electric arc iurnace regulator system comprising operating means for adjusting an electrode with relation to a charge to be heated, control means for starting and stopping said operating means to adjust said electrode, said control means having an intermediate position in which said control means is ineffective to adjust the electrode, a pair oi: opposed coils for operating said control means,-connections for energizing one of said coils in response to the voltage between said electrode and the charge, connections for energizing the other of said coils across the electrode supply circuit whereby said control means is operated to adjust theelectrode so as to maintain a predetermined relation between the voltage from the electrode to the charge and the voltage or the electrode supply circuit, and means responsive to failure of the power supply to the electrode for returning said control means to said intermediate position.

3. A regulator system for iurnaces provided with at least two electrodes comprising operating means for adjusting one of, said electrodes, controlmeans responsive to an electrical condition of the electrode circuit for starting and stopping said operating means to adjust the electrod said control means having an intermediate position in which said control means is ineffective to adjust the electrode, a pair of opposed coils for operating said control means, connections for energizing one of said coils inresponse to an electrical condition of the electrode circuit, connections for energizing the other of said coils from the voltage across said electrodes whereby said control means is operated to eiiect adjustment of the electrode so as to maintain a predetermined relation between said electrical condition and the supply source voltage, and means for biasing said control means to said intermediate position to prevent adjustment of the electrode in the event of failure of the electrode supply source.

4. An electric furnace regulator system comprising a motor for adjusting an electrode for heating a charge, a pair of normally open switches for controlling said motor to raise or lower the electrode, a control member for said switches having an intermediate open circuit position, a pair of coils acting in opposition to each other for moving said control member to control said switches, connections for energizing one of said coils in response to the voltage supplied to said electrode, connections for energizing the other of said coils in response to the voltage from the electrode to the charge whereby said control means is operated to adjust the electrode so as to maintain a predetermined relation between the voltage from the electrode to the charge and the voltage supplied to the electrode, and means for moving said control member to said neutral position in the event oi failure of. the voltage supply to said electrode.

5. An electric furnace regulator system comprising a motor for adjusting an electrode, a pair ofreversing switches for controlling the operation of said motor, operating coils for said switches, control means responsive to an electrical condition of the electrode circuit for controlling the circuit of said coils, said control means having an intermediate neutral position in which said motor is deenergized, a pair of opposed coils for operating said control means, connections for energizing one of said coils in response to an electrical condition of the electrode circuit, connections i'or energizing the other of said coils from the voltage of the electrode supply circuit whereby said control means is operated to effect adjustment the electrode so as to maintain a predetermined relation between said electrical condition and the voltage of the electrode supply circuit, means responsive to failure of the electrode supply source for returning said control means to said intermediate position, and antihunting means for assisting in the return 01 said HUMAN R. STANSEL. 

